I couldn't find the 40mm parts here, so I used 1.25 inch iron pipe. You can get pre-threaded pipe nipples (yes, that's what plumbers call stubby pieces of pipe), end-caps and ther rest of the parts in any local hardware store. Used a few layers of electrical tape for insulation. Otherwise, the design, parts and construction were the same.

The iron pipe must conduct heat a little faster than plastic. Mine thawed out in about 2.5 hours.

I think that the material you use for the main part makes a difference in the time the lock takes to thaw. I'm looking for stainless steel and aluminum pipe/end caps to experiment.

Also, I'm going to try using a light chain instead of rope for the part that is frozen inside. I've clipped one ring from a dog choke collar, leaving the other ring intact. The chain feeds through the 6mm hole smoothly. I haven't tried it yet, but it looks like it will work. I'd guess that the chain will conduct heat faster and will thaw out quicker.

The material used to insulate the lock should also make a difference in thaw times. Need to experiment with that too.

Your design solves a lot of problems and is easy modify. Thanks for the devious idea!

Aluminium/stainless steel is a good material, but it will be colder to touch, unless, indeed, wrapped in something what does not conduct heat. I was also thinking about chains, but abandoned the idea, because using chains will lead to cold water leakage I would like to avoid.

But if you don't care about the temperature and leaking, steel pipes and chains would make a really good and rigid construction. The chain must be able to easily slide out of the tube, of course :-)

hey hey firt to say what a super idea i just made one myself and its drying now i made one without the rubber socket and its a little smaller i still have to test it but i will so i will let you know how long it will take to melt and how it feels i have also got some pictures of it.

grr I so need one of these! The commercial one doesn't come close in justifying the $200 price tag...
Such a pity that I don't have the skills to construct something as simple as this!! lol I wish someone can make me one and I'll pay for it